Weighted drill collar



Jan. 26, 1965 H. C. HUMPHREY WEIGI-ITED DRILL COLLAR Filed Dec. 19, 1961ate'rit Ofilice 3,167,137 harmed Jan. 26, 1965 3,167,137 WEIGHTED DRILLCOLLAR Howard C. Humphrey, Liberty, Tex., assignor to Texaco Inc., NewYork, N .Y., a corporation of Delaware Filed Dec. 19, 1961, Ser. No.160,508 3 Claims. (Cl. 175-320) This invention relates generally to welldrilling and Specifically is concerned with an improvement in drillingtools.

In rotary drilling, the bit is rotated, with weight being applied to itin order to obtain effective cutting. As the well bore increases indepth, lengths of drill pipe, each 30 feet long are added to form thedrill stern. Through this drill pipe, drilling fluid is provided to thebottom of the well bore, where the bit cuttings are picked up andbrought to the surface.

Frequently, these cuttings and other detritus form such a compact massat the bottom of the well bore that the drilling fluid is unable tocarry such matter awa, the drill stern becomes wedged in the well boreand is unable to rotate the bit for further drilling. When such anincident occurs, as much as possible of the drill stem is salvaged byunscrewing individual lengths of the drill pipe and the remainder of thedrill stem is abandoned.

This is an expensive proposition since the drill stern adjacent the bitcomprises the drill collar, which is distinct from the drill pipe. Thiscollar is essential to drilling operations because it functions throughits weight and rigidity to keep the hole straight. It keeps weight onthe big without compression on the drill pipe and thereby aids inavoiding hole deviation.

The drill pipe, on the other hand, transmits torque, circulates mud, andis relatively too flexible to contribute much weight at the bottom ofthe drill hole without bendmg.

Conventional drill collars are made of solid steel billets to obtain thenecessary weight, with the center machined out to the desired insidediameter. A costly limitation is associated with this method ofconstruction because the outside diameters often are large enough toprevent adequate washing over in those cases where the drill collarsbecome stuck.

These collars are commonly 30 feet in length, with from 1 to 20 of themjoined together for drilling a single well through soft formations,while up to 40 or more may be required for hard formation drilling. Eachcollar ranges in cost from $500 to $1000 or more, so that it becomesexpensive whendrill collars have to be abandoned when the drill stembecomes stuck. The conventional drill collar ranges in inside diameterfrom 1 /2" to 4" and outside diameter from 4%" to 8%".

There is no fixed rule for the relationship of the outside diameter of adrill collar to the diameter of drill pipe used. The essential thing isto use a drill collar whose diameter will permit a standard casing sizeinside diameter to slip over it, if washing-over becomes neces- ,sary.The inside diameter of the Wash pipe will also have to be large enoughto pass over the drill pipe joints and pipe protectors. In other words,the outside diameter of a drill collar should be that of a diameter lessthan the diameter of well bore which will permit a Wash-over pipe 1manufacture.

Still another object of invention is to provide an improved drill collarwhich is more susceptible to salvage and recovery operations.

These and other objects, advantages and features of the presentinvention will become apparent from the following description of theinventiton and by reference to the accompanying drawing wherein:

FIG. 1 is a partial diagrammatic vertical section of a prior art borehole indicating a typical condition therein; and

FIG. 2 is a cross section of my improved drill collar.

In accordance with the illustrated embodiment of my invention, there isshown a composite structure in which an annulus formed by spaced, hightensile tubes is filled with an alloy having a specific gravity greaterthan conventional steel to provide the required weight in a drillcollar; and a method for constructing the same is disclosed.

Referring to FIG. 1, a typical prior art bore hole extending into theearth is disclosed at 10, in which the drilling means are shown ascomprising a string of drill pipe 11, connected to the drill collar 12,to the lower end of which is secured a rotary drill bit 13, which, uponrotation of the drilling means, produces the bore hole. As an example,when drilling at approximately 9,000 feet, a 12%" or 12 /2" bit would beattached to a 7%" outside diameter drill collar string, which, in turn,would be attached to a 5" drill pipe string. As the drilling progresses,cuttings and other chips 14, removed by the bit 13, accumulate at thebottom of the bore hole and are carried to the surface and deposited ina manner well known and so not fully illustrated here.

FIG. 2 discloses the composite drill collar 20, as comprising tooljoints or threaded end sections, with the section having the externaltaper threaded pin at 21 and the section having the internal taperthreaded socket at 22. High tensile strength, tubular steel pipes, shownat 23 and 24, the latter with internal taper threaded ends, respectivelyform the inner and outer walls of the drill collar, and are fastened tothe end sections, either by screw threading and/ or welding, therebydefining an an nular chamber. Because of the relatively long length ofthechamber (about 30) as compared with its short diameter (about 8"),centering guides between the inner and outer pipes are used; Theseguides, shown at 30, are

. and the pipes 23 and 24 and by the welds at 23a and 24a,

and by the threaded connection 22a between tool joint 22 and pipe'24 andby the weld connections between tool joint 22 and the pipes 23 and 24 at23b and 24b. The notch welds at 24a and 24b lock the screw joints andprevent any backing off or unscrewing.

The spacing guides 30, fixed to either one of the pipes, serve not onlyas partial partitions but also as anchors to hold the lead filling inposition and thus preserve the bond to the filling exposed surfaces ofthe pipe to prevent independent motions between the pipeand the leadfilling and to provide continuity in the cross section of the compositedrill collar. If necessary, the surfaces of the pipe to be exposed tothe lead filling may be treated specially in order to obtain a betterbond between the lead filling and the spaced pipe. i

The drill collar can be fabricated to any dimension for use in drilling,and usually is based on standard size drill pipe. Thus, when such acomposite drill collar, using standard size drill pipe, is attached to adrill string of drill pipe having the same outer diametral dimension asthe a composite drill collar, then the drill string would have a uniformouter diametral dimension (see FIGURE 2). When a 7 inch outside diameterpipe is used with a 2 /2 inch drill pipe centered internally, with bothjoined to 7 inch tool joints or end sections and the annulus thus formedfilled with lead or a lead alloy, the following comparison of dimensionsand weights of drill collars illustrates the advantages to be gained:

Conven- Improved tional Drill Drill Collar Collar Outside diameter,inches 7% 7 Wgt. with 2 I.D., lbs... 4, 500 4, 600

Table 1 Type J-55 N-SO P-llO Minimum yield strength (p.s.i.) 55, 00080,000 110,000 Average yield factor (p.s.i.) G5, 000 85,000 123, 000Minimum tensile strength (p.s.i.) 75, 000 100, 000 125, 000

With the use of a conventional 7%" drill collar for drilling a 9%" borehole, the clearance on'each side of the drill collar is 1 In the eventthe drill collar becomes stuck, this small clearance to get over thedrill collar with a rotary shoe and wash pipe in order to Wash over andclear away the wedged detritus between the drill collar and the borehole is such'that more failures to complete the wash over than successesresult.

With the improved drill collar, having an out-side diameter of 7", theclearance on each side is 17 which is enough to permit the rotary shoeand wash pipe to wash over it and clear out the detritus.

The weights and strengths of materials used are also advantageous. Steelspecific gravities fall in the approximate range of 8.2 and lower, whilelead and lead alloys fall in the range of 9.4 to 11.3. ASTM Grade19leadbase Babbitt has a tensile strength of 10,000 p.s.i. as compared tothe tensile strength of 1,500 psi. for cast lead. Thisparticular Babbittcontains about tin, 9% antimony and 86% lead. A comparative lead alloywith antimony has a tensile strength of 8,000 p.s.i.

One method of fabricating the disclosed composite drill collaris tofasten the inner pipe of the drill collar to a composite or built-upA.P.I. threaded pipe joint, either by welding, as shown at 23b, FIG. -2,or alternatively, by a screw thread joint and an anchor weld to lock thejoint, as shown at 21a, 23a, FIG. 2. The spacing guides or spiders (30,F-IG. 2) are fastened as by flash welding, either to the outer surfaceof the inner pipe or the inner surface of the outer pipe. Then, the partof the drill collar assembly with the pipe joint would be positioned andcentered in the outer tubes, which makes up the external part of thedrill collar, the pipes being spaced apart from each other by thecentering guides. This partial assembly 'then is lowered into a rat holein a metal fabricating shop, and the annulus between the spaced pipes ispoured full of molten'lead ora lead alloy. After cooling of the pouredmaterial, the other fabricated A.P.I. tool joint is attached to thepartial assembly in a similar manner, either by threading and/ orwelding. In the case of a threaded connection, a notch weld providespositive locking of the screw joint, as shown at 24a, FIG. 2.

The disclosed drill collar is an improvement over that disclosed andclaimed in my prior Patent No. 2,958,512, issued on November 1, 1960.

Thus, there has been disclosed and described a novel method and improveddrill collar made thereby which is adapted to be attached to the drillstring of drill pipe having the same outer diametral dimension, and whencompared with the conventional drill collar, is relatively easy tosalvage, is less'costly to fabricate, and has greater weight withsmaller outside diameter.

Obviously, other modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

I claim: a

-1. In combination, in a drill collar of composite construction subjectto rotation, end sections and inner and outer pipe members joinedtheretoin concentrically spaced relationship to each other thereby defining anannular chamber therewith, said drill collar being adapted to beattached to a rotatable drill pipe string having the same outerdiametral dimension, each of said end sections having the SEIIHC OUtB Ydiametral dimension as the outer pipe member and having a passageway incoaxial comend sections to provide a drill collar of substantially thesame or greater weight and of lesser outer diametral dimension incomparison with a conventional integral drill collar, said metallicmaterial being selected from the group consisting pf lead and an alloyof lead having a specific gravity ranging from 9.4 to 11.3, and aplurality of resilient metallic members fixedly fastened to and spacedalong the length of one of said pipe members within said annularchamber, said metallic members projecting equidistantly from said one ofsaid pipe members'into contact with the other of said pipe members forconcentric positioning of said pipe members with respect to each other,said metallic members being imbedded in said metallic material to serveas anchors therefor.

2. In a drill collar in accordance withclaim 1, said end sections andsaid outer pipe member are taper threaded for fastening to each other,and a weld at the external end of each of the screw joints between saidend sections and said outer pipe member seals each of said joints andprevents unscrewing.

3. In a drill collar in accordancewith claim 1, said inner and outerpipe members comprise standard size drill pipe, said inner and outerpipe members being lock fas tened to said end sections by welds.

References Cited in the file of this patent UNITED STATES PATENTSJackson Jan. 8,

1. IN COMBINATION, IN A DRILL COLLAR OF COMPOSITE CONSTRUCTION SUBJECTTO ROTATION, END SECTIONS AND INNER AND OUTER PIPE MEMBERS JOINEDTHERETO IN CONCENTRICALLY SPACED RELATIONSHIP TO EACH OTHER THREREBYDEFINING AN ANNULAR CHAMBER THEREWITH, SAID DRILL COLLAR BEING ADAPTEDTO BE ATTACHED TO A ROTATABLE DRILL PIPE STRING HAVING THE SAME OUTERDIAMETRICAL DIMENSION, EACH OF SAID SECTIONS HAVING THE SAME OUTERDIAMETRICAL DIMENSION AS THE OUTER PIPE MEMBER AND HAVING A PASSAGEWAYIN COAXIAL COMMUNICATION WITH AND WITH A DIAMETER EQUAL TO THE INNERDIAMETER OF THE INNER PIPE MEMBER, A METALLIC MATERIAL COMPLETELYOCCUPYING SAID ANNULAR CHAMBER AND HAVING A HIGHER SPECIFIC GRAVITY THANSAID PIPE MEMBERS AND SAID END SECTIONS TO PROVIDE A DRILL COLAR OFSUBSTANTIALLY THE